Tank Average Fuel Economy Issue

Has anyone else had issues with the Tank Average Fuel Economy? I wish it was right but I've recently started seeing a 5-6 MPG increase in my economy and I know it's not correct.

This weekend, I went about 83 miles on a full tank and then topped off to see if I was correct, and I was as it took a little over 4 gallons (~20 MPG but my screen was saying around 25).

Any thoughts? I'm due for my 5k service next week and was going to bring it up there but thought I'd ask the experts first.

Thanks fellow Taco owners!

 

Got 25 most of last week driving around town (mix of hills and a few stops) on a stock offroad. Shifting has improved a bit too now that I'm over the 3K mark. Either that or I have just gotten used to it.

 

Consider how a gas pump "auto shutoff" works.
When the tank is nearly full, the air coming up the filler tube enters a venturi in the gas pump handle; which, in turn, causes a mechanical device in the gas pump handle to stop the flow of fuel. Not all handle sensors are equally sensitive, so you may pump a little more or a little less gas than expected.

Also, if your vehicle was tilted at all, the tank could accept a little more or a little less gas than expected.

Bottom line:
When filling your tank, specially when topping it off with only a few gallons, the accuracy of the pump shut-off is reduced. That is why, when measuring MPG, you should always fill your tank at the same pump, same station every time ... and try to fill it when it really needs filling, rather than when it needs only a few gallons.

 

Out of curiosity...is that what the system is saying or what you've confirmed?

 

Thanks old-timer. I understand exactly what you're saying and I didn't think my few gallon fill up would be completely accurate. The part I didn't explain is that I was under half a tank, sitting in a parking lot with the car running while I was looking around the setups. I didn't change anything major and suddenly I jumped from 19MPG to 24MPG while not moving and have stayed that high since then.

I'm not expecting 100% accuracy but something is wrong and I was wondering if anyone else's MPG estimates have gone wrong in the system. I've always been at 19-20MPG and I'm suddenly at 26MPG.

 

Mine's always high by about .5 to 1mpg. It's not off by that much. The service department isn't going to be able to do anything to address this.

 

Warm(er) weather is probably accounting for the majority of 1-3 mpg gains people were seeing vs. the winter. 5 or 6 mpgs is something wonky in the system. Also, adding 4 gals is not a very good measure of how much was used. You really need to do calcs on nearly full (10+ gal) fill-ups.

 

Daniel--I've heard some very similar things, that it's always a little high. However, you don't think Toyota needs to do something if they're computer system in the vehicle isn't working? I'm just curious because it seems to me the calculation is part of the functionality I purchased with the truck and if it's not working...

And I'm not trying to argue, just trying to understand your point.

 

Thanks, and I completely agree about my measurement but I was anxious because something just started going wrong. I'm going to do my regular driving and fill-up this time to see...but my MPGs are already incredibly high again.

I appreciate the input but what I'm hearing is that no one has experienced this issue as I stayed between 19-20 MPG for the first 4,500 miles and suddenly a jump to 25-26 (when I know there's no way that's correct).

 

Have you ever driven a vehicle in which this system is completely accurate? I certainly have not.

 

My first vehicle with this type of functionality, and I'm no expert on either vehicles or this type of functionality...no problem admitting that.

However, when the range jumps like that for no reason, I'm concerned and seems fairly obvious that something is wrong (maybe a sensor or who knows what else). The bottom line is the average was reasonably close to accurate and now it's off by 25-30%.

 

I have constantly been getting 19-22 mpg city highway etc, and has been checked by manual calculations.
Just hit around 5000k on truck and the tanks are getting better, best yet 670km when light came on.
(416miles)

 

It's the same technology that's been around since the 70's and 80's, without much improvement. I've had close to 20 cars with a similar feature, and none of them were 100% accurate. It's roundabout information. Even your vehicles odometer is allowed by law to be inaccurate up to a certain percentage, and I'm sure the trip computer gets it's mileage information from the same slightly inaccurate odometer.

I'd think you would need to run through a few tanks before you make the determination that it's off by 30%. It's extraordinarily unlikely that a sensor has failed, causing a slight fluctuation of the trip computer information.

 

I have the opposite problem. My computer shows I'm averaging 15mpg but when I did my calculations manually I had 18mpg.

 

Daniel--You keep talking about the average never being 100% accurate and that's not what I'm saying. I'm not sure where the confusion lies with our communication, maybe I'm just taking it the wrong way but it just seems like you're telling me not to worry about it and telling me the history of the calculations. I get that I shouldn't rush to a conclusion because of 1 tank being off and I'm not, hence the questions here to see if anyone else has experienced a similar issue...but I'm not one to wait until something goes completely wrong either. I am currently running a completely full tank to see what the actual calculations are, but I cannot believe I'm magically getting 6 MPGs more...seems fairly obvious that something is wrong though I'd be happy if I'm wrong and the new MPGs is correct. My history is:

• 0 - 4500 miles: Tank Average was between 19-20 MPGs, which is fairly close to accurate and completely acceptable in my humble opinion. And I'd say that 70-80% of the time I was at the same 2 pumps and always got around the same MPGs (regardless of pumps)
• 4500 - 4800 miles: In the middle of a tank within the lower side of that range I was getting the regular 19-20 MPGs and, while sitting in a parking lot with the truck running and messing with a few settings, it jumped from 19-20 MPGs to 25-26 MPGs and all tank history was reset. The MPGs has stayed high even after 2 refills (1 of those was a 4 gallon refill)

My confusion with your responses is that you seem to basically be telling me not to worry about it and I don't understand why you'd say that when this could be symptom of a larger issue. Now I'm not saying there is a larger issue but what if that calculation is being thrown off because something is wrong with the fuel gauge? If it's saying I'm getting 25 MPGs and I'm actually getting 20 MPGs then the vehicle thinks I'm using 1 gallon less per 100 miles so when I get around a quarter a tank remaining, I'm basically empty and then I run out of gas on the road. I'd rather be more paranoid and ask questions than to run out of gas for the first time in 25+ years of driving when some seems wrong with the vehicle.

And I'm not trying to start an argument with you, I hope you're trying to help but I'm confused with your responses and don't worry about it isn't acceptable to me. If you haven't experienced the issue and your recommendation is to not get excited about 1 tank issue, I thank you for recommendation and am already running that test.

 

I guess I just don't see how, in any way, the trip computer could lead you to believe there's an issue with the vehicle. Especially when the inputs to the system are not accurately measured under any circumstance (odometer, fuel level, fuel usage). Even the gas gauge itself is not really accurate, fuel density can vary quite a bit based on many factors.

 

And there's a darn good chance you're right but I'm not just going to say "oh well, that's the way it is now" when it was working much closer to correctly. I want to do what I can to get to the bottom of it...I paid a lot of money for my truck and I expect it to work within certain parameters...everything to work within certain parameters.

Guess we just agree to disagree at the moment.

 

Aye, that is the rub!

Apparently nobody else has complained of the problem (yet), so your observation is unique.
The next step is to try and determine the cause. Perhaps "messing with a few settings" is the culprit.
Suggest you manually calculate your MPG for the current tank, using the odometer and the gas pump's display as data sources (as yet, nobody has shown the odometer is wildly inaccurate, although the trip meters seem to reset for some).

On the less serious side ... maybe you found the magic code to increase MPG!

 

Good call old-timer, I do need to go back through the settings thought I'm 99% certain I didn't do anything with the MPGs calculations (if you can). And I did get a reset of the all my driving history, not the trip though.

I'm working on the manual calculation now...after a 4 gallon fill-up, it showed that average MPGs were wrong but I understand that's not necessarily the best test. I think it was close enough to confirm a potential issue, but I'm working on the more legit test now.

If I can duplicate the "magic"...I'll let everyone know, free of charge.

 

Just curious, do you have an access cab or double cab?